Contamination of shell eggs with microorganisms such as Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella Enteritidis) constitutes a health hazard to consumers, an added liability to the food industry, and an extra burden on governmental agencies involved in regulation and surveillance of the food industry. The fresh egg is one of the most common vehicles for the transmission of Salmonella spp. to humans. Salmonellosis, the food-transmitted disease caused by Salmonella spp., results from the consumption of contaminated shell eggs or products containing egg components. According to some estimates, only 1 in 20,000 raw eggs in the United States are contaminated with Salmonella Enteritidis; however, Salmonella transmission through contaminated eggs results in 700,000 cases of salmonellosis and costs approximately $1.1 billion annually.
The primary objectives of food sanitation include reducing the levels of microorganisms in food and preventing or limiting their proliferation in contaminated food items. Food sanitation typically involves applying one or more established decontamination procedures to various food items. Cleaning eggs by washing is a common practice, which is required in plants operating under the Federal Grading Service (USDA, 2004). Egg washers currently used in the food industry spray the eggs with water that contains commercially-available sanitizers and detergents. A variety of procedures have been developed to control or eliminate Salmonella Enteritidis in eggs; however, available methods are time consuming, uneconomical and may be only partially effective. Proposed alternative decontamination methods include the use of thermal treatments, gamma radiation, chlorine and iodine, hydrogen peroxide, ultraviolet (UV) radiation, pulsed light, gas plasma, electrolyzed oxidative water, and ozone.
Short-wave UV radiation is known to be effective against microorganisms that are airborne, on food surfaces, or in liquids. Treatment with UV radiation has been shown to effectively reduce the contamination of shell eggs by aerobic bacteria, yeasts and molds, and Salmonella Typhimurium. Additionally, heat treatment has been utilized to sanitize the egg surface and to eliminate internal Salmonella Enteritidis. Ozone (O3) is known to be a strong and highly reactive antimicrobial agent. Ozone has been extensively studied for potential applications in the food industry for ensuring the safety of food products such as meat, poultry, fish, fruits and vegetables, cheese, and many other foods. Ozone has also been tested in decontaminating hatcheries, hatching eggs, poultry chill water, and poultry carcass. The literature indicates that both gaseous and aqueous ozone inactivate many poultry pathogens that potentially contaminate the surface of shell eggs, setters, and hatchers. Ozone has been reported to have a relative eggshell penetrability of 68.1% and has been shown to have a synergistic effect when used in combination with carbon dioxide. Advantageously, ozone spontaneously decomposes into non-toxic oxygen and the United States Food and Drug Administration (FDA) has recently approved the broad use of ozone in foods (CFR, 2001).
Despite the approaches discussed above, currently there are no low-temperature treatments capable of effectively sanitizing egg surface, nor methods to inactivate Salmonella inside shell eggs without impacting overall egg quality. Low temperatures are known to preserve the quality and safety of shell eggs during production, storage, transportation and retail. Maintaining the shell eggs at low temperatures may also significantly reduce the incidence of Salmonella Enteritidis egg-related illnesses. Thus, there is a need for more economic, effective treatments for inactivating Salmonella inside and on the surface of shell eggs without compromising the quality of the eggs being treated.